Folding method of airbag

ABSTRACT

A folding method of an airbag having a left airbag portion and a right airbag portion is disclosed. In one form, the method includes the steps of: a primary folding step for forming a primary folded body in which said airbag is flattened along a top-bottom direction and along a right-left direction by folding said airbag in a manner that decreases a thickness of said left airbag portion and said right airbag portion along a front-back direction and at least partially separates a left surface of said left airbag portion and a right surface of said right airbag portion along the right-left direction; and a secondary folding step for forming a final folded body by folding said primary folded body in a manner that decreases its width along the top-bottom direction and along the right-left direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. JP2009-190279 filed on Aug. 19, 2009, the entire contentof which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a folding method of an airbag forrestraining an occupant in the event of a vehicle collision or the like.The present invention, more particularly, relates to a folding method ofan airbag having a left airbag portion and a right airbag portion thatinflate in front of the occupant, on the left side and the right side,respectively. Note that, in this invention, the front-back direction andthe horizontal direction correspond to the front-back direction andhorizontal direction for the occupant.

BACKGROUND OF THE INVENTION

Airbags that restrain an occupant in the event of a vehicle collision orthe like include an airbag that has a left airbag portion and a rightairbag portion that inflate in front of the occupant on the left sideand the right side, respectively. These left and right airbag portionsare inflated by a common inflator. A folding method of this airbag isdescribed in JP, A, 2007-45190.

In the prior art, when the airbag is to be folded, first the left airbagportion and the right airbag portion are each placed sideways. The leftairbag portion and the right airbag portion are then respectivelyflattened in a top-bottom direction and front-back direction. Next, theleft airbag portion is folded from the upper end and lower end towardthe center along the top-bottom direction into a roll or accordion shapealong the top-bottom direction, thereby forming a long, narrowstrip-shape in the front-back direction. Similarly, the right airbagportion is folded from the upper end and lower end toward the centerinto a roll or accordion shape along the top-bottom direction, therebyforming a long, narrow strip-shape in the front-back direction.Subsequently, each of these folded bodies of the left and right airbagportions is folded in a manner that decreases the length in thefront-back direction, thereby forming a final folded body of a blockshape.

In the prior art, once the left and right airbag portions are foldedinto long, narrow strip-shapes in the front-back direction, each portionis folded in a manner that decreases its length in the front-backdirection. In consequence, when the airbag is inflated, the left andright airbag portions first unfold and deploy in the front-backdirection, and subsequently unfold and deploy in the vertical direction,and subsequently deploy in a manner that increases its width in thehorizontal direction. As a result, once the airbag begins inflating, arelatively long period of time is required for the left and right airbagportions to deploy across a wide range in the vertical and horizontaldirections.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a foldingmethod of an airbag that permits deployment of the left and right airbagportions across a wide range in the top-bottom and right-left directionsin a short period of time once the airbag begins to inflate.

In order to acheive the above-mentioned object, according to the firstinvention, there is provided a folding method of an airbag comprising aleft airbag portion that inflates on the left side in front of anoccupant, and a right airbag portion that inflates on the right side infront of an occupant, comprising the steps of: a primary folding stepfor forming a primary folded body in which the airbag is substantiallyflattened along a top-bottom direction and along a right-left directionby folding the airbag in a manner that decreases a thickness of the leftairbag portion and the right airbag portion along a substantiallyfront-back direction and at least partially separates a left surface ofthe left airbag portion and a right surface of the right airbag portionalong the right-left direction; and a secondary folding step for forminga final folded body by folding the primary folded body in a manner thatdecreases its width substantially along the top-bottom direction andalong the right-left direction.

According to the second invention, in the folding method of an airbagaccording to the first invention, in the secondary folding step, anupper end portion, a lower end portion, a left end portion, and a rightend portion of the primary folded body are each folded toward a centerof the primary folded body along the top-bottom direction and along theright-left direction.

According to the third invention, in the folding method of an airbagaccording to the second invention, in the secondary folding step, atleast one of an upper end portion, a lower end portion, a left endportion, and a right end portion of the primary folded body is foldedtoward a center of the primary folded body into a roll shape along thetop-bottom direction and along the right-left direction.

According to the fourth invention, in the folding method of an airbagaccording to the first invention, in the secondary folding step, theprimary folded body is folded in a manner that decreases its width alongthe right-left direction, and subsequently folded in a manner thatdecreases its width along the top-bottom direction.

According to the fifth invention, in the folding method of an airbagaccording to the fourth invention, in the secondary folding step, theprimary folded body is folded in a manner that decreases its width alongthe top-bottom direction by respectively folding an upper end portionand a lower end portion of the primary folded body toward a center ofthe primary folded body along the top-bottom direction, and thenpositioning a folded body of the upper end portion on a top side of afolded body of the lower end portion.

According to the sixth invention, in the folding method of an airbagaccording to the fifth invention, the airbag inflates from an instrumentpanel of a vehicle toward the vehicle rear, bringing the airbag close toan occupant, and further comprises a hollow portion disposed between theleft airbag portion and the right airbag portion, that passessubstantially vertically through the airbag when the airbag is in aninflated state; and at least a part of the hollow portion is positionedfurther toward the vehicle rear than an end portion of an instrumentpanel on the vehicle rear side when the airbag is in an inflated state.

According to the seventh invention, in the folding method of an airbagaccording to the first invention, the airbag further comprisesconnecting members including a connect member that is provided at aintermediate part of the left airbag portion along the front-backdirection at the time of inflation and connects left and right lateralsurfaces of the left airbag portion, and another connecting member thatis provided at a intermediate part of the right airbag portion along thefront-back direction at the time of inflation and connects left andright lateral surfaces of the right airbag portion; and in the primaryfolding step, the airbag is extended along the right-left direction byalong the right-left direction separating an end of a left surface ofthe left airbag portion that is further rearward than the connectingmembers and an end of a right surface of the right airbag portion thatis further rearward than the connecting members, and along theright-left direction separating an end of a left surface of the leftairbag portion that is further frontward than the connecting members andan end of a right surface of the right airbag portion that is furtherfrontward than the connecting members.

According to the eighth invention, in the folding method of an airbagaccording to the seventh invention, in the secondary folding step, anend portion of the left airbag portion that is further rearward than theconnecting members and an end portion of the right airbag portion thatis further rearward than the connecting members are folded toward acenter of the primary folded body along the right-left direction, and anend portion of the left airbag portion that is further frontward thanthe connecting members and an end portion of the right airbag portionthat is further frontward that the connecting members are folded towarda center of the primary folded body along the right-left direction.

According to the folding method of the airbag of the present invention,the airbag is first folded in a manner that decreases the thickness ofthe left and right airbag portions in a substantially front-backdirection and at least partially separates the left surface of the leftairbag portion and the right surface of the right airbag portion along aright-left direction. With this arrangement, a primary folded body thatis flattened in the substantially top-bottom and right-left directionsis formed (primary folding step). Subsequently, this primary folded bodyis folded in a manner that decreases its width in the substantiallytop-bottom and right-left directions, thereby forming a final foldedbody (secondary folding step). As a result, when the airbag starts toinflate, the airbag first unfolds and deploys in the top-bottom andright-left directions and subsequently increases in thickness in thefront-back direction. With this arrangement, after inflation begins, theairbag is capable of deploying across a wide range in the top-bottom andright-left directions in a short period of time. As a result, even in acase where the airbag starts inflating with the occupant seatedrelatively forward, causing the occupant to contact the airbag in theearly stages while the airbag is being inflated, the airbag is capableof receiving the body of the occupant across a wide range. With thisarrangement, when the occupant contacts the airbag during inflation, theload locally applied to the head and neck regions of the occupant issuppressed,

In the present invention, during airbag inflation, the left airbagportion inflates on the front left side of the occupant to receive theleft side of the thorax of the occupant, and the right airbag portioninflates on the front right side of the occupant to receive the rightside of the thorax of the occupant. Since hard, strong ribs exist in theleft and right sides of the thorax, the left and right airbag portionsare capable of securely receiving the occupant.

In the secondary folding step, the upper end, lower end, left end, andright end of the primary folded body are each preferably folded towardthe center of the primary folded body along the top-bottom direction andthe right-left direction. When thus folded, at the time of inflation theairbag inflates quickly and substantially evenly along a top-bottomdirection and along a right-left direction.

In this case, the upper end, lower end, left end, and right end of theprimary folded body of the airbag are preferably at least partiallyfolded into a roll toward the center of the primary folded body alongthe top-bottom direction and the right-left direction. When the airbagis thus folded, at the time of inflation the portions folded into a rollinflate and deploy while unrolling toward the outside of the airbag. Atthis time, inflation continues in order from the unrolled portions,causing the portions folded into a roll to inflate substantially equallyin the axial direction and substantially parallel direction of therolls. That is, the upper end and lower end of the primary folded bodyinflate substantially equally in the right-left direction, and the leftend and right end of the primary folded body inflate substantiallyequally in the top-bottom direction.

In the secondary folding step, once the primary folded body is folded ina manner that decreases its width along the right-left direction, thatfolded primary folded body may be folded in a mariner that decreases itswidth along the top-bottom direction. In such a case, once the airbagstarts to inflate, the airbag quickly inflates along the top-bottomdirection.

In such a case, in the secondary folding step, once the upper and lowerends of the primary folded body are each folded toward the center of theprimary folded body along the top-bottom direction, the folded body ofthe upper end is preferably positioned above the folded body of thelower end, thereby decreasing the width of the primary folded body alongthe top-bottom direction. When the airbag is thus folded, the upper endof the airbag deploys faster than the lower end, causing the airbag todeploy in front of the head and thorax regions of the occupant in ashort period of time. With this arrangement, even if an object ispresent in the vicinity of the airbag device installation area such asthe instrument panel when the airbag inflates, for example, the airbaginflates and deploys toward the vehicle rear, passing over the object.As a result, the invention keeps the inflating airbag from excessivelypressing the object located in the vicinity of the airbag deviceinstallation area toward the rear.

This folding method is ideally applied to airbags having theconfiguration described below. That is, the folding method is ideallyapplied to airbags configured so that a hollow portion that passessubstantially vertically through the inflated airbag is provided betweenthe left and right airbag portions, and at least a part of the lower endof the hollow portion is positioned further toward the vehicle rear thanthe end of the instrument panel on the vehicle rear side when the airbagin an inflated state. With this airbag, even if an object is present inthe vicinity of the instrument panel when the airbag inflates, theobject is engulfed in the hollow portion. When the airbag is foldedusing the above folding method, when the airbag inflates, the airbaginflates and deploys toward the vehicle rear, passing over the objectlocated in the vicinity of the instrument panel as described above.Subsequently, the airbag inflates downward, covering the object fromabove, thereby engulfing the object in the hollow portion of the airbag.

Additionally, the airbag may be provided with connecting members in theintermediate part of the left airbag portion and the right airbagportion in the front-back direction at the time of inflation,respectively, that connect the left and right surfaces of the leftairbag portion, and the left and right surfaces of the right airbagportion. In such a case, in the primary folding step, the airbag ispreferably along a right-left direction extended by along a right-leftdirection separating the ends of the left and right airbag portions thatare further rearward than the connecting members of the left surface ofthe left airbag portion and the right surface of the right airbagportion, and along a right-left direction separating the ends of theleft and right airbag portions that are further frontward than theconnecting members of the left surface of the left airbag portion andthe right surface of the right airbag portion. With the airbag thusfolded, the airbag is capable of sufficiently extending in theright-left direction, even when the airbag is provided with connectingmembers that connect the lateral surfaces of the left and right airbagportions.

In such a case, in the secondary folding step, the ends of the left andright airbag portions that are further rearward than the connectingmembers are preferably folded toward the center of the primary foldedbody along the right-left direction, and the ends of the left and rightairbag portions that are further frontward than the connecting membersare preferably folded toward the center of the primary folded body alongthe right-left direction. With the airbag thus folded, when the airbaginflates, the ends of the left and right airbag portions that arefurther rearward than the connecting members and the ends of the leftand right airbag portions that are further frontward than the connectingmembers each deploy along a right-left direction, resulting in quickdeployment of the airbag in the horizontal direction. Accordingly, theends of the left and right airbag portions that are further rearwardthan the connecting members and the ends of the left and right airbagportions that are further frontward than the connecting members eachinflate in a manner that increases the thickness in the front-backdirection. As a result, quick deployment of the airbag in the front-backdirection is achieved as well,

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the airbag to be folded using thefolding method of an airbag according to an embodiment of the presentinvention.

FIG. 2 is a cross-sectional view taken along section II-II in FIG. 1.

FIG. 3 is a cross-sectional view taken along section in FIG. 2.

FIG. 4 is a cross-sectional view of the same section as FIG. 2,illustrating the primary folding method of the airbag.

FIG. 5A is a front view of the primary folded body of the airbag.

FIG. 5B is a cross-sectional view taken along section B-B in FIG. 5A.

FIG. 5C is a cross-sectional view taken along section C-C in FIG. 5A.

FIG. 6 is a rear view of the primary folded body of the airbag.

FIG. 7A is a front view illustrating the secondary folding method of theairbag.

FIG. 7B is a cross-sectional view taken along section B-B in FIG. 7A.

FIG. 8A is a front view illustrating the secondary folding method of theairbag.

FIG. 8B is a cross-sectional view taken along section B-B in FIG. 8A.

FIG. 9A is a front view illustrating the secondary folding method of theairbag.

FIG. 9B is a cross-sectional view taken along section B-B in FIG. 9A.

FIG. 10A is a front view illustrating the secondary folding method ofthe airbag.

FIG. 10B is a cross-sectional view taken along section B-B in FIG. 10A.

FIG. 11A is a front view illustrating the secondary folding method ofthe airbag.

FIG. 11B is a cross-sectional view taken along section B-B in FIG. 11A.

FIG. 12A is a front view illustrating the secondary folding method ofthe airbag.

FIG. 12B is a cross-sectional view taken along section B-B in FIG. 12A.

FIG. 13A is a front view illustrating the secondary folding method ofthe airbag.

FIG. 13B is a cross-sectional view taken along section B-B in FIG. 13A.

FIG. 14 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 15 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 16 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 17 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 18 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 19 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 20 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 21 is a cross-sectional view of the same section as FIG. 13B,illustrating the secondary folding method of the airbag.

FIG. 22 is a cross-sectional view of the same section as FIG. 13B,illustrating the final folded shape of the airbag.

FIG. 23 is a side view at the time of airbag inflation and a top view atthe time of airbag inflation.

FIG. 24 is a side view of the airbag during inflation, and a side viewof the fully inflated airbag.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to accompanying drawings.

FIG. 1 is a perspective view of the airbag to be folded using thefolding method of an airbag according to the embodiment. FIG. 2 is across-sectional view taken along line 1141 in FIG. 1. FIG. 3 is across-sectional view taken along line in FIG. 2. FIG. 4 is across-sectional view of the same section as FIG. 2, illustrating theprimary folding method of the airbag. FIG. 5A is a front view of theprimary folded body of the airbag, FIG. 5B is a cross-sectional viewtaken along line B-B in FIG. 5A, and FIG. 5C is a cross-sectional viewtaken along line C-C in FIG. 5A. FIG. 6 is a rear view of the primaryfolded body of the airbag. FIG. 7A to FIG. 21 are explanatory views ofthe secondary folding method of the airbag. Note that FIG. 7A, FIG. 8A,FIG. 9A, FIG. 10A, FIG. 11A, FIG. 12A, and FIG. 13A are front views ofthe airbag; and FIG. 7B, FIG. 8B, FIG. 9B, FIG. 10B, FIG. 11B, FIG. 12B,and FIG. 13B are cross-sectional views taken along line B-B of FIG. 7A,FIG. 8A, FIG. 9A, FIG. 10A, FIG. 11A, FIG. 12A, and FIG. 13A,respectively. In FIG. 5B, FIG. 7B, FIG. 8B, FIG. 9B, FIG. 10B, FIG. 11B,and FIG. 12B, the image of the connecting bands for restraining thehorizontal widths of the right and left airbag portions during inflationis omitted. FIG. 14 to FIG. 21 are cross-sectional views of the samesection as FIG. 13B. FIG. 22 is a cross-sectional view of the samesection as FIG. 13B, illustrating the final folded shape of the airbag.FIG. 23A is a side view of the inflated airbag, and FIG. 23B is a topview of the inflated airbag. FIG, 24A is a side view of the airbagduring inflation, and FIG. 24B is a side view of the fully inflatedairbag. Note that FIG. 23A and FIG. 23B illustrate a state where theoccupant is positioned relatively forward, and FIG. 24A and FIG. 24Billustrate a state where an object (including the occupant) is presentin the vicinity of the instrument panel.

In the description below, the front-back direction and horizontaldirection correspond to the front-back direction and horizontaldirection for the occupant of the vehicle, respectively. Additionally,the phrase “mountain-fold the airbag” means to fold the airbag so thatthe folding line extends outward toward the outside of the airbag, andthe phrase “valley-fold the airbag” means to fold the airbag so that thefolding line extends inward toward the inside of the airbag.

In this embodiment, an airbag 10 is a passenger seat airbag provided toa passenger seat airbag device for restraining a passenger seat occupantof a vehicle. As illustrated in FIG. 23A and FIG. 23B, the passengerseat airbag device comprises the airbag 10, a retainer 2 of an upperopening container shape that is positioned in a dashboard 1 in front ofthe passenger seat of the vehicle and houses the folded airbag 10, aninflator 3 for inflating the airbag 10, and a strip-shaped shape-holdingsheet 4 for holding the shape of the folded body of the airbag 10 (referto FIG. 22). Reference numeral 6 denotes a windshield above theinstrument panel 1. The retainer 2 is disposed behind the instrumentpanel 1. A door portion (not shown) that opens when the airbag 10inflates, permitting inflation and emergence into the vehicle interiorof the airbag 10, is formed on the instrument panel 1. Note that the lid(lid material) formed separately from the instrument panel 1 issometimes mounted to the upper opening of the retainer 2.

The airbag 10 comprises a right airbag portion 11 that inflates on theright side in front of the occupant, a left airbag portion 12 thatinflates on the left side in front of the occupant, and a base-endchamber 13 that passes through the base end of the right airbag portion11 and the left airbag portion 12. A gas inlet 13 a that introduces gasfrom the inflator 3 is provided on the front end of the bottom of thebase-end chamber 13.

A press plate 7 for connecting the airbag 10 to the retainer 2 isoverlaid on the periphery portion of the gas inlet 13 a from inside thebase-end chamber 13. From the press plate 7, a plurality of stud bolts 7a is provided. Each of the stud bolts 7 a passes through the peripheryportion of the gas inlet 13 a and extends to the outside of the airbag10. A substantially cylindrical inflator holding portion 7 b for holdingthe cylindrical inflator 3 is provided on the press plate 7.

The gas from the inflator 3 is introduced from the gas inlet 13 a intothe base-end chamber 13, inflating the base-end chamber 13, andsubsequently introduced from the base-end chamber 13 into the rightairbag portion 11 and the left airbag portion 12, inflating the rightairbag portion 11 and the left airbag portion 12. A vent hole 14 isprovided to both the right surface of the inflated right airbag portion11 and the left surface of the inflated left airbag portion 12(hereinafter sometimes referred to as the outer lateral surfaces of theright airbag portion 11 and the left airbag portion 12).

In this embodiment, within the region of the surfaces of the rightairbag portion 11 and the left airbag portion 12 that face each other atthe time of inflation, the intermediate part of the left surface of theright airbag portion 11 in the front-back direction and the intermediatepart of the right surface of the left airbag portion 12 in thefront-back direction are stitched together by a seam 15. This seam 15extends in a circular shape as illustrated by FIG. 2 and FIG. 3. On thesurfaces that face each other, the seam 15 makes a circle more towardthe center in the vertical direction and front-back direction than onthe upper surface, lower surface, or rear surface (the surface faced theoccupant) of the right airbag portion 11 and the left airbag portion 12in an inflated state. With this arrangement, a continuous recessedportion 16 between the upper surfaces, the lower surfaces, and the rearsurfaces of the right airbag portion 11 and the left airbag portion 12is formed when the right airbag portion 11 and the left airbag portion12 are in an inflated state.

When the airbag 10 is fully inflated, the recessed portion 16 openstoward the occupant (that is, toward the right in FIG. 1 to FIG. 4)since a connecting member such as a tie panel does not exist between therear end parts of the right airbag portion 11 and the left airbagportion 12. The inmost part of the recessed portion 16 is the seam 15.When this airbag 10 is fully inflated, as shown in FIG. 2, a distance Wbetween an aft end lit of the right airbag portion 11 and an aft end 12t of the left airbag portion 14 is preferably 150 to 450 mm, morepreferably 170 to 430 mm. Further, when this airbag 10 is fullyinflated, a depth D (refer to FIG. 3) of the recessed portion 16 on therear surface of the right air bag portion 11 and the left airbag portion12 is preferably 25 to 400 mm, more preferably 50 to 350 mm.

As illustrated in FIG. 3, the front end of the seam 15 is separated fromthe rear end of the base-end chamber 13. A hollow portion 17 that passessubstantially vertically through the right airbag portion 11 and theleft airbag portion 12 exists between the front end of the seam 15 andthe rear end of the base-end chamber 13. As illustrated in FIG. 3, themore the hollow portion 17 is in a lower end from the verticalintermediate part of the hollow portion 17, the more a width of thehollow portion 17 along the front-back direction is greater when theright airbag portion 11 and the left airbag portion 12 are inflated.With this hollow portion 17, the depth of the recessed portion 16 on thelower surface of the right airbag portion 11 and the left airbag portion12 increases all the way to the base-end chamber 13. As illustrated inFIG. 24B, when the airbag 10 is fully inflated, at least a part of thelower end of the hollow portion 17 is positioned further toward thevehicle rear than a rear end portion 1 a of the instrument panel 1. Thatis, with the airbag 10 fully inflated, at least one part of the openingon the lower end of the hollow portion 17 is exposed on the lowersurface of the airbag 10, closer to the vehicle rear than the rear endportion 1 a of the instrument panel 1. Therefore, as shown in FIG. 24B,even if an object C is present in the vicinity of the instrument panel 1when the airbag 10 inflates, the object C is engulfed by the hollowportion 17.

In this embodiment, a connecting band 18 is provided as a connectingmember to both the right airbag portion 11 and the left airbag portion12, near the middle in both the vertical direction and front-backdirection at the time of inflation, to connect the lateral surfaces ofthe right airbag portion 11 and the left airbag portion 12 and restrictthe horizontal width during inflation. As illustrated in FIG. 2, theconnecting bands 18 are disposed so that they cross in the substantiallyright-left direction inside the right airbag portion 11 and the leftairbag portion 12, respectively, and both ends connect to the left andright surfaces of the right airbag portion 11 and the left airbagportion 12, respectively.

As illustrated in FIG. 2, each of the connecting bands 18 comprises afirst band member 18 a having one end connected to the left surface ofthe right airbag portion 11 or the right surface of the left airbagportion 12 (that is, the face-to-face surfaces), and a second bandmember 18 b having one end connected to the right surface of the rightairbag portion 11 or the left surface of the left airbag portion 12(that is, the outer lateral surfaces). The other end of the band member18 a and the other end of the band member 18 b are joined inside theright airbag portion 11 and inside the left airbag portion 12,respectively. With this arrangement, each of the connecting bands 18connects the lateral surface of the right airbag portion 11 and thelateral surface of the left airbag portion 12. Reference numeral 18 cdenotes a seam that stitches together one end of each of the first bandmembers 18 a with the surface facing the right airbag portion 11 and theleft airbag portion 12, respectively. Reference numeral 18 d denotes aseam that stitches together one end of each of the second band members18 b with the outer lateral surface of the right airbag portion 11 andthe left airbag portion 12, respectively. Reference numeral 18 e denotesa seam that stitches together the other end of the right airbag portion11 with the other end of the left airbag portion 12. Reference numeral19 (refer to FIG. 1) denotes a reinforcing fabric that reinforces thestitched part of each of the second band members 18 h and the rightairbag portion 11 and the outer lateral surface of the left airbagportion 12. In this embodiment, one end of the first band member 18 ainside the right airbag portion 11 and one end of the first band member18 a inside the left airbag portion 12 sandwich the surfaces of theright airbag portion 11 and the left airbag portion 12 that face eachother, and are stitched together by a common seam 18 c. The seam 15 thatis the inmost part of the recessed portion 16 surrounds this seam 18 c.

When the airbag 10 is folded, the airbag 10 is first folded in a mannerthat decreases the thickness of the right airbag portion 11 and the leftairbag portion 12 in the substantially front-back direction, and atleast partially separates the right surface of the right airbag portion11 and the left surface of the left airbag portion 12 along a right-leftdirection, as illustrated in FIGS. 4 to 6. With this arrangement, aprimary folded body 10A that is flattened along the top-bottom directionand the right-left direction is formed (primary folding step).Subsequently, this primary folded body 10A is folded in a manner thatdecreases its width along the top-bottom direction and the right-leftdirection to form a final folded body 10C, as illustrated in FIG. 7A toFIG. 20 (secondary folding step). The folding method of the airbag 10will now be described in detail.

Primary Folding Step

When the airbag 10 is to be subjected to the primary folding process,the airbag 10 is placed on a substantially horizontal table with thebase-end chamber 13 (or the rear end of the right airbag portion 11 andthe left airbag portion 12) at the bottom, for example. Then, whileextending the airbag 10 in the right-left direction, the airbag 10 isflattened in the substantially front-back direction (in thesubstantially top-bottom direction when placed on the table as describedabove; hereinafter the same).

At this time, in this embodiment, the intermediate part of the rightsurface of the right airbag portion 11 in the front-back direction andthe intermediate part of the left surface of the left airbag portion 12in the front-back direction are each valley-folded along a substantiallytop-bottom (substantially right-left with the airbag 10 placed on thetable as described above) folding line L₁ of the airbag 10, and theintermediate part of the right surface of the right airbag portion 11 inthe front-back direction and the intermediate part of the left surfaceof the left airbag portion 12 in the front-back direction are broughtnear the surfaces of the right airbag portion 11 and the left airbagportion 12 that face each other, as illustrated in FIG. 4 and FIG. 5C.Note that while in this embodiment the folding line L₁ is positioned onthe right surface of the right airbag portion 11 and the left surface ofthe left airbag portion 12, slightly further toward the rear end of theright airbag portion 11 and the left airbag portion 12 than the seam 18d that stitches together each of the connecting bands 18, the positionof the folding line L₁ is not limited thereto.

Additionally, the area of the right surface of the right airbag portion11 and the area of the left surface of the left airbag portion 12 thatare near the center between the folding line L₁ and the inner-most areaof the recessed portion 16 on the rear surface of the airbag 10 (thatis, the rear end of the seam 15) are each pulled along a right-leftdirection to separate the area near the center of the right airbagportion 11 and the area near the center of the left airbag portion 12,while creating a mountain-fold along a substantially top-bottom foldingline L₂. Note that this folding line L₂ , is positioned on the rightsurface of the right airbag portion 11 and the left surface of the leftairbag portion 12, further on the rear end of the right airbag portion11 and the left airbag portion 12 than the seam 18 d. With thisarrangement, the airbag 10 is flattened along a right-left direction sothat the ends of the right airbag portion 11 and the left airbag portion12 that are further rearward than the folding line L₁ are separated fromthe seam 15. Hereinafter, these extending parts will be referred to as arear-end extending portion 11 a of the right airbag portion 11, and arear-end extending portion 12 a of the left airbag portion 12.

Further, the area of the right surface of the right airbag portion 11and the area of the left surface of the left airbag portion 12 that arenear the center between the folding line L₁ and the rear end of thebase-end chamber 13 are each pulled along a right-left direction toseparate the area near the center of the right airbag portion 11 and thearea near the center of the left airbag portion 12, while creating amountain-fold along the substantially top-bottom folding line L₃. Notethat this folding line L₃ is positioned on the right surface of theright airbag portion 11 and the left surface of the left airbag portion12, further on the front end of the right airbag portion 11 and the leftairbag portion 12 than the seam 18 d. At this time, the area of theportion where the surfaces of the right airbag portion 11 and the leftairbag portion 12 meet, which surrounds the hollow portion 17 and isbetween the front end of the seam 15 and the crotch part of the meetingsurfaces, is extended and flattened along a right-left direction, asillustrated in FIG. 4. With this arrangement, the ends of the rightairbag portion 11 and the left airbag portion 12 that are fartherfrontward than the folding line L₁ are flattened along a right-leftdirection. Hereinafter, these portions will be referred to as afront-end extending portion 11 b of the right airbag portion 11, and afront-end extending portion 12 b of the left airbag portion 12.

Furthermore, the base-end chamber 13 is folded along the front surfaceof the front end extending portions 11 b and 12 b of the right airbagportion 11 and the left airbag portion 12 At this time, in thisembodiment, the base-end chamber 13 is flattened and folded in thesubstantially top-bottom direction while its left and right surfaces arefolded to the inside thereof to form a strip shape, and subsequentlythis strip-shaped base-end chamber 13 is folded to the front surface ofthe front-end extending portions 11 b and 12 b, as illustrated in FIG.4. At this time, a portion 13 b of the strip-shaped base-end chamber 13that is further rearward than the gas inlet 13 a is along a top-bottomdirection folded back into a zigzag shape along the front surface of thefront-end extending portions 11 b and 12 b as necessary, as illustratedin FIG. 5B and FIG. 6. With this arrangement, the gas inlet 13 a ispositioned near the substantial center of the front-end extendingportions 11 b and 12 b along the top-bottom direction. Note that, inthis case, the portion 13 b of the base-end chamber 13 that is furtherrearward than the gas inlet 13 a is preferably folded back in part tothe region that is further upward than the substantial center of thefront-end extending portions 11 b and 12 b along the top-bottomdirection.

In a case where slack develops on the front surfaces of the front-endextending portions 11 b and 12 b when the base-end chamber 13 is thusfolded back to the front surfaces of the front-end extending portions 11b and 12 b, the areas near the center of the front surfaces of thefront-end extending portions 11 b and 12 b along the top-bottomdirection are folded back in a zigzag shape (Z-shape) alongsubstantially right-left folding lines L₄ and L₅ to form a tuck, asillustrated in FIG. 6. Then, those same areas are partially folded tothe inside of the right airbag portion 11 and the left airbag portion12, thereby removing the slack along the top-bottom direction on thefront surfaces of the front end extending portions 11 b and 12 b.Additionally, the area near the center of the front surfaces of thefront-end extending portions 11 b and 12 b along the right-leftdirection is valley-folded along a top-bottom folding line L₆ to removethe slack along the right-left direction on the front surfaces of thefront-end extending portions 11 b and 12 b. Then, folding is performedfrom the base toward the left or right onto the front surfaces of thefront-end extending portions 11 b and 12 b. In FIG. 6, this area isfolded between the front surfaces of the front-end extending portions 11b and 12 b and the folded body of the base-end chamber 13. It should benoted, however, that the treatment of the slack on the front surfaces ofthe front-end extending portions 11 b and 12 b is not limited thereto.

Thus folded, the airbag 10 forms the primary folded body 10A that isflattened along the top-bottom direction and the right-left direction.

Secondary Folding Step

In this embodiment, when the primary folded body 10A is to be subjectedto the secondary folding process, first the primary folded body 10A isfolded in a manner that decreases the width of the right airbag portion11 and the left airbag portion 12 (the front-end extending portions 11 band 12 b and the rear-end extending portions 11 a and 12 a) along theright-left direction as illustrated in FIG. 7A to FIG. 12B, andsubsequently folded in a manner that decreases the width thereof alongthe top-bottom direction as illustrated in FIG. 13A to FIG. 20A.

Specifically, as illustrated in FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B,first the front-end extending portion 12 b of the left airbag portion 12is folded back toward the center of the primary folded body 10A alongthe right-left direction along substantially top-bottom folding lines L₇and L₈ from the left end at a predetermined width, forming a roll-shapedfolded body. Note that while the front-end extending portion 12 b isfolded back twice in FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B, thefront-end extending portion 12 b may be folded once or three or moretimes. In such a case, as illustrated in FIG. 7B, and FIG. 8B, thefront-end extending portion 12 b is folded back toward the rear surfacethereof, and this roll-shaped folded body of the front-end extendingportion 12 b is positioned between the folded body of the base-endchamber 13 and the rear-end extending portion 12 a.

Next, as illustrated in FIG. 9A, FIG. 9B, FIG. 10A, and FIG. 10B, thefront-end extending portion 11 b of the right airbag portion 11 isfolded in the same manner as the front-end extending portion 12 b of theleft airbag portion 12. That is, the front-end extending portion 11 b ofthe right airbag portion 11 is folded back toward the center of theprimary folded body 10A along the right-left direction alongsubstantially top-bottom folding lines L₉ and L₁₀ from the right endthereof at a predetermined width, forming a roll-shaped folded body.Note that while the front-end extending portion 11 b is folded twice inFIG. 9A, FIG. 9B, FIG. 10A, and FIG. 10B, the front-end extendingportion 11 b may be folded once or three or more times. In such a case,as illustrated in FIG. 9B, and FIG. 10B, the front-end extending portion11 b is folded back toward the rear surface thereof, and thisroll-shaped folded body of the front-end extending portion 11 b ispositioned between the folded body of the base-end chamber 13 and therear-end extending portion 11 a.

It should be noted, however, that the order in which the front-endextending portions 11 b and 12 b are folded is not limited thereto. Forexample, first the front-end extending portion 11 b of the right airbagportion 11 may be folded into a roll-shape and then the front-endextending portion 12 b of the left airbag portion 12 may be folded intoa roll-shape.

Next, as illustrated in FIG. 11A and FIG. 11B, the left end of therear-end extending portion 12 a of the left airbag portion 12 is foldedback toward the center of the primary folded body 10A along theright-left direction along a substantially top-bottom folding line L₁₁,up to the part of the front-end extending portion 12 b that sticks outfurther leftward than the roll-shaped folded body. Note, however, thatwhile the left end of the rear-end extending portion 12 a is folded backonly once, the left end may be folded back twice or more times. In sucha case, as illustrated in FIG. 11B, the left end of the rear-endextending portion 12 a is folded back to the front surface thereof, andpositioned between the roll-shaped folded body of the front-endextending portion 12 b and the part of the rear-end extending portion 12a that is further toward the right end than the folding line L₁₁.

Next, as illustrated in FIG. 12A and FIG. 12B, the rear-end extendingportion 11 a of the right airbag portion 11 is folded in the same manneras the rear-end extending portion 12 a of the left airbag portion 12.That is, the right end of the rear-end extending portion 11 a of theright airbag portion 11 is folded back toward the center of the primaryfolded body 10A along the right-left direction along a substantiallytop-bottom folding line L₁₂, up to the part of the front-end extendingportion 11 b that sticks out further rightward than the roll-shapedbody. Note, however, that while the right end of the rear-end extendingportion 11 a is folded back only once, the right end may be folded backtwice or more times. In such a case, as illustrated in FIG. 12B, theright end of the rear-end extending portion 11 a is folded back to thefront surface thereof, and positioned between the roll-shaped foldedbody of the front-end extending portion 11 b and the part of therear-end extending portion 11 a that is further toward the left end thanthe folding line L₁₂.

It should be noted, however, that the order in which the rear-endextending portions 11 a and 12 a are folded is not limited thereto. Forexample, first the rear-end extending portion 11 a of the right airbagportion 11 may be folded and then the rear-end extending portion 12 a ofthe left airbag portion 12 may be folded.

With this arrangement, the top-bottom folding of the primary folded body10A is completed, and the airbag 10 is formed into along a top-bottomdirection long and narrow strip-shaped intermediate folded body 10B.

Next, as illustrated in FIG. 13A to FIG. 15, the strip-shapedintermediate folded body 10B is folded back to the front surface alongsubstantially right-left folding lines L₁₃, L¹⁴, and L₁₅ from the lowerend thereof to the height of the area near the lower edge of the pressplate 7, at a predetermined width, to form a roll-shaped folded body R₁.Note that, while the lower end of the intermediate folded body 10B isfolded back three times in FIG. 13A to FIG. 15, the lower end may befolded back once or four or more times.

Next, as illustrated in FIG. 16, the lower end of the intermediatefolded body 10B is folded back to the rear surface along a substantiallyright-left folding line L₁₆ at the height near the lower edge of thepress plate 7, and the roll-shaped folded body R₁ is positioned on therear surface near the center of the intermediate folded body 10B alongthe top-bottom direction.

Next, as illustrated in FIG. 17 to FIG. 19, the intermediate folded body10B is folded back to the front surface along substantially right-leftfolding lines L₁₇, L₁₈, and L₁₉ from the upper end thereof to the heightof the area near the upper edge of the press plate 7, at a predeterminedwidth, to form a roll-shaped folded body R₂. Note that, while the upperend of the intermediate folded body 10B is folded back three times inFIG. 17 to FIG. 19, the upper end may be folded back once or four ormore times.

Next, as illustrated in FIG. 20, the upper end of the intermediatefolded body 10B is folded back to the rear surface along a substantiallyright-left folding line L₂₀ at the height near the upper edge of thepress plate 7, and the roll-shaped folded body R₂ of this upper end ispositioned further toward the rear surface of the previously foldedroll-shaped folded body R) of the lower end.

Next, as illustrated in FIG. 21, the part of the base-end chamber 13that is further toward the front end than the press plate 7 (thefront-end portion when the airbag 10 is inflated; the end that isfurther upward than the upper edge of the press plate 7 of theintermediate folded body 10B in FIG. 20) is folded rearward along asubstantially right-left folding line L₂₁ near the upper edge of thepress plate 7, onto the upper surface of the roll-shaped folded body R₁.

Thus subjected to the secondary folding process, the airbag 10 forms theblock-shaped final folded body 10C, as illustrated in FIG. 21.

Subsequently, as illustrated in FIG. 21 and FIG. 22, the shape-holdingsheet 4 is wrapped around the airbag final folded body 10C, and the endthereof is attached to the stud bolts 7 a. With this arrangement, theshape of the airbag final folded body 10C is held by the shape-holdingsheet 4.

This folded body 10C of the airbag 10 is sent to the airbag deviceassembly process. In the airbag device assembly process, the inflatorholding portion 7 b of the press plate 7 is installed to the inflator 3,the inflator 3 and the folded body 10C of the airbag 10 are positionedinside the retainer 2, and the press plate 7 is connected to the bottomsurface of the retainer 2 by the stud bolts 7 a, thereby completing thepassenger seat airbag device. Note that, as described above, a lid (notshown) is mounted to the upper opening of the retainer 2 as necessary.

The folded body 10C of the airbag 10, as illustrated in FIG. 22, isdisposed inside the retainer 2 with the base-end chamber 13 downward andthe end of the base-end chamber 13 that is further toward the front endthan the press plate 7 placed on the vehicle front side of theroll-shaped folded body R₁ on the lower end of the right airbag portion11 and the left airbag portion 12. With this arrangement, theroll-shaped folded body R₂ on the upper end of the right airbag portion11 and the left airbag portion 12 is disposed above the roll-shapedfolded body R₁ on the lower end, inside the retainer 2.

The operation of the passenger seat airbag device comprising this airbag10 will now be described.

When a vehicle equipped with this airbag device is involved in acollision, the inflator 3 ejects gas. The gas from the inflator 3 isfirst introduced into the base-end chamber 13, inflating the base-endchamber 13. The inflation pressure of the airbag 10 breaks theshape-holding sheet 4, causing the door portion (or lid) of theinstrument panel 1 to break open and form an opening for the emergingairbag. The airbag 10 then inflates through this opening and into thevehicle interior.

The gas introduced into the base-chamber 13 subsequently flows insidethe right airbag portion 11 and the left airbag portion 12. With thisarrangement, the right airbag portion 11 inflates on the front rightside of the occupant, and the left airbag portion 12 inflates on thefront left side of the occupant. The inflated right airbag portion 11receives the right side of the thorax of the occupant, and the inflatedleft airbag portion 12 receives the left side of the thorax of theoccupant, with the breastbone region facing the recessed portion 16therebetween. As a result, the reaction force applied near thebreastbones during airbag reception decreases. Additionally, the headportion of the occupant enters and is received by the recessed portion16.

According to the folding method of an airbag of the present invention,as described above, the airbag 10 is first folded in a manner thatdecreases the thickness of the right airbag portion 11 and the leftairbag portion 12 in the substantially front-back direction, and atleast partially separates the right surface of the right airbag portion11 and the left surface of the left airbag portion 12 along a right-leftdirection, thereby forming the primary folded body 10A that is flattenedalong the top-bottom direction and the right-left direction.Subsequently, the primary folded body 10A is folded in a manner thatdecreases its width along the right-left direction, thereby forming thealong a top-bottom direction long and narrow strip-shaped intermediatefolded body 10B. Subsequently, this intermediate folded body 10B isfolded in a manner that decreases its width along the top-bottomdirection, thereby forming the final folded body 10C. As a result, whenthe airbag 10 begins to inflate, the airbag 10 deploys in a manner thatunfolds and deploys the top-bottom folds along a top-bottom direction,subsequently unfolds and deploys the right-left folds along a right-leftdirection, and subsequently increases the thickness in the front-backdirection. With this arrangement, once inflation begins, the airbag 10can be deployed across a wide range along the top-bottom direction andthe right-left direction in a short period of time. As a result, in acase where the airbag 10 starts inflating with the occupant seatedrelatively forward causing the occupant to contact the airbag 10 in theearly stages while the airbag 10 is being inflated, as illustrated inFIG. 23A and FIG. 23B, for example, the airbag 10 receives the shouldersand thorax portion of the occupant across a wide range. With thisarrangement, when the occupant contacts the airbag 10 during inflation,the load locally applied to the head and neck regions of the occupant issuppressed. Note that the chain double-dashed lines in FIG. 23A and FIG.23B denote a silhouette of the airbag 10 when it is fully inflated.

According to this embodiment, in the secondary folding step, the upperend, lower end, left end, and right end of the primary folded body 10Aare each folded toward the center of the primary folded body 10A alongthe top-bottom direction and the right-left direction. With thisarrangement, at the time of inflation, the airbag 10 inflates quicklyand substantially evenly vertically and horizontally.

According to this embodiment, in the secondary folding step, the upperend, lower end, left end, and right end of the primary folded body 10Aof the airbag 10 are each folded into a roll shape toward the center ofthe primary folded body 10A along the top-bottom direction and theright-left direction. As a result, when the airbag 10 inflates, theupper end and lower end roll upward and downward, respectively,inflating and deploying while unrolling, and the left end and right endroll leftward and rightward, respectively, inflating and deploying whileunrolling. When each of the upper, lower, left, and right ends of therolled airbag 10 inflates, the end inflates starting from the unrolledportion, causing these portions to inflate substantially evenly in theaxial direction and substantially parallel direction of the roll-shapedfold. That is, in this embodiment, the upper and lower ends of theprimary folded body 10A inflate substantially equally in the horizontaldirection, and the left and right ends of the primary folded body 10Ainflate substantially equally in the vertical direction.

According to this embodiment, in the secondary folding step, the primaryfolded body 10A is folded in a manner that decreases its width along theright-left direction, thereby forming the intermediate folded body 10B,and then the intermediate folded body 10B is folded in a manner thatdecreases its width along the top-bottom direction. With thisarrangement, once inflation begins, the airbag 10 inflates quickly inthe vertical direction.

Further, according to this embodiment, the lower end and the upper endof the intermediate folded body 10B are each folded into a roll, and theroll-shaped folded body R₂ of the upper end is disposed upward from theroll-shaped folded body R₁ of the lower end. As a result, when theairbag 10 begins to inflate, the roll-shaped folded body R₂ of the upperend of the airbag 10 is pressed from the retainer 2 into the vehicleinterior before the roll-shaped folded body R₁ of the lower end, makingthe upper end of the airbag 10 inflate and deploy more quickly than thelower end. With this arrangement, the airbag 10 is capable of deployingin front of the head portion and thorax portion of the occupant in ashort period of time. Additionally, with this arrangement, even if theobject C is present in the vicinity of the instrument panel 1 asillustrated in FIG. 24A, for example, the airbag 10 inflates and deploystoward the vehicle rear, passing over the object C. As a result, theinvention keeps the inflating airbag 10 from excessively pressing theobject C located in the vicinity of the instrument panel 1 toward therear. Subsequently, as illustrated in FIG. 24B, the lower end of theairbag 10 inflates, causing the object C to be engulfed in the hollowportion 17 and to be restrained by the airbag 10. At this time, theairbag 10 inflates downward covering the object C from above, therebyengulfing the object C in the hollow portion 17.

According to this embodiment, the airbag 10 is provided with theconnecting bands 18 at the intermediate part of the right airbag portion11 in the front-back direction at the time of inflation, that connectthe left and right surfaces of the right airbag portion 11.Additionally, the airbag 10 is provided with the connecting bands 18 atthe intermediate part of the left airbag portion 12 in the front-backdirection at the time of inflation, that connect the left and rightsurfaces of the left airbag portion 12. In the primary folding step, thepart of the right surface of the right airbag portion 11 that ispositioned further toward the rear end of the right airbag portion 11and the left airbag portion 12 than the connecting bands 18, and thepart of the left surface of the left airbag portion 12 that ispositioned further toward the rear end of the right airbag portion 11and the left airbag portion 12 than the connecting bands 18 are along aright-left direction separated. Further, the part of the right surfaceof the right airbag portion 11 that is positioned further toward thefront end of the right airbag portion 11 and the left airbag portion 12than the connecting bands 18, and the part of the left surface of theleft airbag portion 12 that is positioned further toward the front endthan the right airbag portion 11 and the left airbag portion 12 than theconnecting bands 18 are along a right-left direction separated. Withthis arrangement, the airbag 10 is extended along a right-leftdirection. By folding the airbag 10 is this manner, the airbag 10 can besufficiently extended along a right-left direction, even if the airbag10 is provided with connecting bands 18 that connect the left and rightsurfaces of the right airbag portion 11 and the left and right surfacesof the left airbag portion 12.

According to this embodiment, in the secondary folding step, the part ofthe right airbag portion 11 that is further toward the rear end than theconnecting bands 18 and the part of the left airbag portion 12 that isfurther toward the rear end than the connecting bands 18 (that is, therear-end extending portion 11 a and the rear-end extending portion 12 a)are folded toward the center of the primary folded body 10A along theright-left direction, Additionally, the part of the right airbag portion11 that is further toward the front end than the connecting bands 18 andthe part of the left airbag portion 12 that is further toward the frontend than the connecting bands 18 (that is, the front-end extendingportion 11 b and the front-end extending portion 12 b) are folded towardthe center of the primary folded body 10A along the right-leftdirection. When the airbag 10 is thus folded, at the time of inflation,the rear-end extending portion 11 a of the right airbag portion 11 andthe rear-end extending portion 12 a of the left airbag portion 12, andthe front-end extending portion 11 b of the right airbag portion 11 andthe front-end extending portion 12 b of the left airbag portion 12respectively deploy along a right-left direction. As a result, quickdeployment of the airbag 10 in the horizontal direction is achieved.Additionally, along with the horizontal deployment of the rear-endextending portions 11 a and 12 a and the front-end extending portions 11b and 12 b, the rear-end extending portions 11 a and 12 a and thefront-end extending portions 11 b and 12 b inflate, increasing therespective thicknesses in the front-back direction. As a result, quickdeployment of the airbag 10 in the front-back direction is alsoachieved.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention may be practiced in various other forms.

For example, while in the above embodiment the upper end, lower end,left end, and right end of the primary folded body 10A of the airbag 10are all folded into a roll-shape, at least a part of these may be foldedinto an accordion-shape.

What is claimed is:
 1. A folding method of an airbag comprising a baseend chamber in which an inflator is disposed, a left airbag portionopening to the base end chamber for receiving inflation gas from theinflator therein to inflate on the left side in front of an occupant,and a right airbag portion opening to the base end chamber for receivinginflation gas from the inflator therein to inflate on the right side infront of an occupant, comprising the steps of: a primary folding stepfor forming a primary folded body in which said airbag is substantiallyflattened along a top-bottom direction and along a right-left directionby folding said airbag in a manner that decreases a thickness of saidleft airbag portion and said right airbag portion along a substantiallyfront-back direction and at least partially separates a left surface ofsaid left airbag portion and a right surface of said right airbagportion along the right-left direction; and a secondary folding step forforming a final folded body by folding said primary folded body in amanner that decreases its width substantially along the top-bottomdirection and along the right-left direction, wherein in said secondaryfolding step, an upper end portion, a lower end portion, a left endportion, and a right end portion of said primary folded body are eachfolded toward a center of said primary folded body along the top-bottomdirection and along the right-left direction, at least one of an upperend portion, a lower end portion, a left end portion, and a right endportion of said primary folded body is folded toward a center of saidprimary folded body into a roll shape along the top-bottom direction andalong the right-left direction, said primary folded body is folded in amanner that decreases its width along the right-left direction, andsubsequently folded in a manner that decreases its width along thetop-bottom direction, and wherein said airbag inflates from aninstrument panel of a vehicle toward the vehicle rear, bringing saidairbag close to an occupant, and further comprises a rearward connectionbetween a right surface of the left airbag portion and a left surface ofthe right airbag portion rearwardly of the base end chamber that extendsin the top-bottom direction for the majority of the width of theinflated left and right airbag portions in the top-bottom direction toform a hollow portion disposed between said left airbag portion and saidright airbag portion rearwardly of the base end chamber and forwardly ofthe rearward connection, that passes substantially vertically through anarea surrounded by said airbag when said airbag is in an inflated state;and at least a part of said hollow portion is positioned further towardthe vehicle rear than an end portion of the instrument panel on thevehicle rear side when said airbag is in an inflated state.
 2. Thefolding method of an airbag according to claim 1, wherein: said airbagfurther comprises connecting members including a connecting member thatis provided at a intermediate part of said left airbag portion along thefront-back direction at the time of inflation and connects the left andright surfaces of said left airbag portion, and another connectingmember that is provided at a intermediate part of said right airbagportion along the front-back direction at the time of inflation andconnects the left and right surfaces of said right airbag portion; andin said secondary folding step, an end portion of said left airbagportion that is further rearward than said connecting members and an endportion of said right airbag portion that is further rearward than saidconnecting members are folded toward a center of said primary foldedbody along the right-left direction, and an end portion of said leftairbag portion that is further frontward than said connecting membersand an end portion of said right airbag portion that is further forwardfrontward than said connecting members are folded toward a center ofsaid primary folded body along the right-left direction.
 3. The foldingmethod of an airbag according to claim 2 wherein the rearward connectioncomprises a closed-loop seam between the left airbag portion rightsurface and the right airbag portion left surface that extends in thetop-bottom direction and in the front-back direction about the locationat which the connecting members are connected to the left airbag portionright surface and the right airbag portion left surface.
 4. A foldingmethod of an airbag comprising a base end chamber in which an inflatoris disposed, a left airbag portion opening to the base end chamber forreceiving inflation gas from the inflator therein to inflate on the leftside in front of an occupant, and a right airbag portion opening to thebase end chamber for receiving inflation gas from the inflator thereinto inflate on the right side in front of an occupant, comprising thesteps of: a primary folding step for forming a primary folded body inwhich said airbag is substantially flattened along a top-bottomdirection and along a right-left direction by folding said airbag in amanner that decreases a thickness of said left airbag portion and saidright airbag portion along a substantially front-back direction and atleast partially separates a left surface of said left airbag portion anda right surface of said right airbag portion along the right-leftdirection; and a secondary folding step for forming a final folded bodyby folding said primary folded body in a manner that decreases its widthsubstantially along the top-bottom direction and along the right-leftdirection wherein in said secondary folding step, an upper end portion,a lower end portion, a left end portion, and a right end portion of saidprimary folded body are each folded toward a center of said primaryfolded body along the top-bottom direction and along the right-leftdirection, at least one of an upper end portion, a lower end portion, aleft end portion, and a right end portion of said primary folded body isfolded toward a center of said primary folded body into a roll shapealong the top-bottom direction and along the right-left direction, saidprimary folded body is folded in a manner that decreases its width alongthe right-left direction, and subsequently folded in a manner thatdecreases its width along the top-bottom direction, and wherein saidairbag inflates from an instrument panel of a vehicle toward the vehiclerear, bringing said airbag close to an occupant, and further comprises arearward connection between a right surface of the left airbag portionand a left surface of the right airbag portion rearwardly of the baseend chamber that extends in the top-bottom direction for the majority ofthe width of the inflated left and right airbag portions in thetop-bottom direction to form a hollow portion disposed between said leftairbag portion and said right airbag portion rearwardly of the base endchamber and forwardly of the rearward connection, that passessubstantially vertically through an area surrounded by said airbag whensaid airbag is in an inflated state; and at least a part of said hollowportion is positioned further toward the vehicle rear than an endportion of the instrument panel on the vehicle rear side when saidairbag is in an inflated state, said airbag further comprises connectingmembers including a connecting member that is provided at a intermediatepart of said left airbag portion along the front-back direction at thetime of inflation and connects the left and right surfaces of said leftairbag portion, and another connecting member that is provided at aintermediate part of said right airbag portion along the front-backdirection at the time of inflation and connects the left and rightsurfaces of said right airbag portion; and in said primary folding step,said airbag is extended along the right-left direction by separatingalong the right-left direction an end of a left surface of said leftairbag portion that is further rearward than said connecting members andan end of a right surface of said right airbag portion that is furtherrearward than said connecting members, and separating along theright-left direction an end of a left surface of said left airbagportion that is further frontward than said connecting members and anend of a right surface of said right airbag portion that is furtherfrontward than said connecting members as well as by means of extendingand flattening along the right-left direction a portion where said rightairbag portion and said left airbag portion face each other and surroundsaid hollow portion.
 5. The folding method of an airbag according toclaim 4, wherein: in said secondary folding step, an end portion of saidleft airbag portion that is further rearward than said connectingmembers and an end portion of said right airbag portion that is furtherrearward than said connecting members are folded toward a center of saidprimary folded body along the right-left direction, and an end portionof said left airbag portion that is further frontward than saidconnecting members and an end portion of said right airbag portion thatis further frontward that said connecting members are folded toward acenter of said primary folded body along the right-left direction.